Hypothyroidism

Hypothyroidism is a term used when someone has a lower
than normal level of thyroid hormone in their body, or an underactive
thyroid gland. Hypothyroidism can develop at any point in the lifespan.
Infants can be born with hypothyroidism, and hypothyroidism can develop
in children and adults of any age.

Thyroid hormone is produced in the
thyroid gland, which is a small, butterfly-shaped gland that lies
just under the Adam's apple in the neck. There are two lobes to
the gland, and they lie just in front and at either side of the windpipe
(trachea). The thyroid is part of the body's endocrine system, which
consists of glands that secrete hormones into the bloodstream. To produce
thyroid hormones, the thyroid gland needs iodine, an element contained
in many foods. Almost every cell in the body, from those in the
brain to those in the feet, responds to these thyroid hormones.

The thyroid
gland also produces a hormone, called calcitonin, which may be
involved in the metabolism of bones.

There are two different forms
of thyroid hormone present in the bloodstream. The two forms of
thyroid hormone differ in the number of iodine units or atoms attached
to the hormone. Iodine is a very important component of thyroid
hormone.

Thyroid hormone with four iodine units is abbreviated as T4

Thyroid
hormone with three iodine units is abbreviated as T3

Most thyroid
hormone in the blood is T4, however…

T3 is the form that is
active in the body, not T4.

Certain cells in the body convert
T4 to T3.

Cells respond to thyroid hormone with an increase in
metabolic activity. Metabolic activity, or metabolism, is a term
used to describe the processes in the body that produce energy
and the chemical substances necessary for cells to grow, divide
to form new cells, and perform other vital functions.If there's
not enough thyroid hormone, the body slows down, like taking
one's foot off the accelerator pedal.

When hypothyroidism develops in older children before growth
and development are complete, they may have a shorter-than-average
height or puberty may be delayed. They also may have
symptoms that are more like those found in adults:

Slow heart rate

Tiredness

Inability to tolerate cold

Dry, flaky skin

Puffiness in the face, especially around the eyes

Impaired memory
and difficulty in thinking (which may appear as a new learning
disability)

Emotional depression

Drowsiness, even after sleeping through the
night

Heavy or irregular menstrual periods (in girls at the age
of puberty)

Constipation

Hypothyroidism that occurs in infancy or early childhood is called cretinism.
Babies born with hypothyroidism classically show a number of symptoms
in the first weeks to months of life. At birth, many symptoms are
subtle, though, and can be missed. They include the following:

Prolonged
newborn jaundice (a yellow discoloration of the skin and the
whites of the eyes)

Poor feeding and constipation

Cool, mottled skin

Increased sleepiness

Decreased crying

Larger-than-normal soft spots on the skull

Umbilical hernia (a soft
protrusion around the navel)

A large tongue

Over time, if untreated, other symptoms typically
become apparent in older infants, toddlers, and young children.
The most obvious symptoms observed in these youngsters reflect
insufficient thyroid hormone for growth and development:

For infants born with hypothyroidism, diagnosis
and treatment within the first month or so of life may prevent
any irreversible problems with the child's development. However,
if diagnosis or treatment is delayed until after the first two or three
months of life, permanent problems with the child's development,
such as mental retardation, may be unavoidable.

In the United States,
Canada, and much of the Western world, newborns are routinely screened
for thyroid hormone deficiency. Infants with abnormal screening
tests receive follow-up evaluation for hypothyroidism. Such testing
commonly leads to the correct diagnosis within the first four weeks of
age, and treatment can begin immediately.

Diagnosis later in childhood
is usually based on information from blood tests, which check levels
of thyroid hormones T4, T3, and TSH, among other related substances.
Abnormally low levels of T4 and T3 indicate hypothyroidism is present.

If TSH is present at a higher-than-normal level, the abnormality
is within the thyroid gland. It is not responding properly to TSH.

If TSH is low, the abnormality is within the brain or pituitary
gland. The pituitary is not releasing TSH despite levels of thyroid
hormone low enough that it should do so.

Hypothyroidism present
from birth is called congenital hypothyroidism (congenital means
at birth), or CH. In North America, CH is found in roughly 1
in every 4,000 newborns. Three causes of CH result in permanent
hypothyroidism and require life-long treatment, and these account for
about 90% of all newborns with CH:

Abnormal thyroid gland development includes babies born without a thyroid gland and those whose
thyroid is not functioning (roughly 80% to 85% of cases).

Abnormal
thyroid hormone production is much less common (roughly 10% to
15% of cases). It is often inherited. In the typical instance,
both parents have normal thyroid function but are carriers for the
defective gene. In such cases, the odds are one in four for each
pregnancy that the baby will have CH.

Abnormal development of the
brain or pituitary gland is the least common cause of permanent
CH (fewer than 5% of cases). Some of these rare conditions are
inherited, whereas others show no familial pattern. In all of
these cases, TSH is not produced or released, and the resultant
hypothyroidism is due to lack of thyroid gland stimulation.

About
10% of newborns with CH have a temporary hypothyroidism that
will resolve within days or months, depending on the specific
cause. In almost all of these cases, the hypothyroidism is due to antithyroid
substances that crossed from the mother's bloodstream into the
unborn baby's blood.

Hypothyroidism that develops during childhood
has a number of causes. In general, the older the child, the more
likely it is that the cause will be similar to the causes of hypothyroidism
in adults. Causes of hypothyroidism that develops during childhood
include:

Late appearance of a congenital problem - A congenital
problem is a problem with which a baby is born. But sometimes
these problems may only become apparent later, after the newborn period.
These children may have small or poorly formed thyroid glands that
could not meet the demands of the growing child.

Inhibition of
thyroid hormone production in the thyroid gland - Inability
to produce enough thyroid hormone may reflect poor function of an apparently
normal thyroid gland. In many cases, a cause is eventually determined,
such as too little iodine in the diet or drug side effect.

Some
drugs intended for a nonthyroid condition can cause hypothyroidism
by inhibiting production of thyroid hormone. These include lithium
(used for psychiatric disorders) and iodine-containing drugs
such as amiodarone (used for heart disorders). In older children
especially, antithyroid drugs used to treat those who have hyperthyroidism
can actually cause hypothyroidism. This happens when the drugs
inhibit hormone production too much, and the child moves from having
an overactive thyroid gland to having an underactive one. In
virtually all cases, drug-related hypothyroidism is reversible. If the
dosage of the drug is lowered or the drug discontinued, the hypothyroidism
will disappear. In some cases, however, there may not be a reasonable
alternative drug, and it becomes simpler to treat the hypothyroidism
with thyroid hormone and having the child remain on the original,
hypothyroidism-causing drug.

Permanent thyroid cell loss as a consequence
of a medical treatment - A permanent loss of functional thyroid
tissue may develop after treatment of hyperthyroidism with either
radioactive iodine or surgery (the latter is more commonly used in
children with severe or unresponsive hyperthyroidism). It may also
develop after radiation therapy for cancers of the neck or chest, such
as lymphomas or Hodgkin's disease.

Autoimmune disease - Autoimmune
disorders are the most common cause of thyroid problems.An immune
disorder is one in which the immune system mistakenly directs
an immune "attack" against
its own healthy cells. Antibodies are manufactured and misdirected
against some of the body's own cells. Any condition in which
the body's immune system attacks its own cells is called an autoimmune
disease. Specifically, the immune system makes antibodies (or attack
proteins) that can affect the function of the thyroid. In Hashimoto's
thyroiditis,
the antibodies directly attack and destroy thyroid cells. In Graves'
disease, these antibodies mimic the action of TSH on thyroid
cells. The antibodies act like a switch put into a permanent "on" position.
Thyroid cells are continually stimulated to produce and release
thyroid hormone, even after blood levels become excessive.

Problems
outside the thyroid gland - Hypothyroidism can develop due
to a problem in a nonthyroid part of the endocrine system (namely the
brain or pituitary gland). This type of hypothyroidism, which
does not originate in the thyroid gland, is much less common (perhaps
5% of cases). Almost all of these cases are due to failure of the pituitary
gland to produce or release TSH.

The treatment for hypothyroidism
is simple: Supply the body with the thyroid hormone that isn't
being produced and released by the thyroid gland. Synthetic (artificially
produced) thyroid hormone (T4) is manufactured in a wide range
of strengths so that dosage can be individually tailored for
each person. It is important that an experienced physician oversee treatment,
because the body's need for thyroid hormone varies over the course
of childhood and puberty. A child will usually be started on
a daily dose of thyroid hormone, have it adjusted until a healthy
level of hormone in the blood is reached, and then be monitored
with regular blood tests. Almost all children with hypothyroidism
will require thyroid hormone replacement therapy for the rest
of their lives. Fortunately, thyroid hormone is simple to take,
and the success of therapy is easily monitored by blood tests
for T4 and TSH that can be done throughout adulthood.